Hey everyone, I’m working on a draft for #warning in Swift. I’ve implemented the draft as it stands, and it’s pretty nice to work with.
I’ve pasted it below, and I’d love some feedback! Thanks! — Harlan Haskins #warning Proposal: SE-NNNN <https://github.com/apple/swift-evolution/blob/master/proposals/NNNN-name.md> Author: Harlan Haskins <https://github.com/harlanhaskins> Status: Awaiting review <https://gist.github.com/harlanhaskins/bfe2d56d7655c5bfdb1855eaf00addb4#rationale> Review manager: TBD <https://gist.github.com/harlanhaskins/bfe2d56d7655c5bfdb1855eaf00addb4#introduction>Introduction It's really common for developers to add TODO/FIXME comments in their source code, but there currently isn't a supported facility to make these visible. People have implemented special workarounds <https://bendodson.com/weblog/2014/10/02/showing-todo-as-warning-in-swift-xcode-project/> to coax Xcode into emitting TODOs and FIXMEs as warnings, but there isn't an accessible way to provide arbitrary warnings, and does not work in a non-Xcode environment. <https://gist.github.com/harlanhaskins/bfe2d56d7655c5bfdb1855eaf00addb4#motivation>Motivation A #warning is for something you intend to fix before submitting your code or for writing future tasks that you or your teammates intend to complete later. Because this is such a common programming pattern, Swift should have a similar facility. <https://gist.github.com/harlanhaskins/bfe2d56d7655c5bfdb1855eaf00addb4#proposed-solution>Proposed solution Add #warning(_:) as a new compiler directive that emits a warning diagnostic with the contents, pointing to the start of the message. func configPath() -> String { #warning("TODO: load this more safely") // expected-warning {{TODO: load this more safely}} return Bundle.main().path(forResource: "Config", ofType: "plist")! } <https://gist.github.com/harlanhaskins/bfe2d56d7655c5bfdb1855eaf00addb4#detailed-design>Detailed design This will add two new productions to the Swift grammar: compiler-control-statement → warning-directive warning-directive → #warning( static-string-literal ) Upon parsing this statement, the Swift compiler will immediately emit a warning and discard the statement. If a #warning exists inside a branch of a #if statement that is not taken, then no warning is emitted. #if false #warning(“This won’t exist”) #endif <https://gist.github.com/harlanhaskins/bfe2d56d7655c5bfdb1855eaf00addb4#impact-on-existing-code>Impact on existing code This change is purely additive; no migration will be required. <https://gist.github.com/harlanhaskins/bfe2d56d7655c5bfdb1855eaf00addb4#alternatives-considered>Alternatives considered We could do some kind of comment-parsing based approach to surface TODOs and FIXMEs, but #warning serves as a general-purpose facility for reporting at compile time. Plus, not all TODO or FIXME comments should surface as warnings in the source.
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